Table of Contents

Introduction

The capacity of a tower silo depends on: (a) the compressibility
of the stored material; (b) the total volume of the silo; (c) the
friction between the wall of the silo and the material; and (d)
the ratio of the settled depth of silage to the diameter of the
silo. This Factsheet contains estimates of tower silo capacities
for alfalfa silage, whole-plant corn silage and various types of
high moisture corn based on a series of analyses of silo capacity
carried out at the University of Guelph and on research done at
research establishments in the Netherlands and Sweden. Values shown
are more accurate than those available in previous extension publications.
Most previously published capacity tables overestimate capacities
for corn silage and underestimate those for high moisture corn.

Tables 1 and 2 show the capacities, in tonnes, of most common silo
sizes for alfalfa and whole-plant corn silage. The capacities in
Table 1 were obtained using a friction coefficient of 0.6, a reasonable
estimate for as-cast concrete walls. Table 2 capacities were calculated
using a friction coefficient of 0.4; this coefficient has been found
appropriate for glass-lined steel walls. Concrete silos coated inside
with a hard glass-like coating will probably have capacities approximating
those in Table 2. Badly corroded rough concrete walls, on the other
hand, may well reduce the capacity below that shown in Table 1.

(a) 1
tonne 1000kg: the capacity in tons (2000 lb) can be obtained by
multiplying the capacities in the table by 1.1 (b) moisture content in percent (wet basis)

Table
2. Estimated steel silo capacities for forages, in tonnes.(a)

Silo Diameter
x Settled Depth

Alfalfa
Silage

Corn
Silage

(m)

(ft)

40%

50%(b)

60%

70%

55%

60%

65%

70%

3.7 x 9.1

12 x 30

34

43

56

81

46

52

60

70

12 x 30

3.7 x 12.1

12 x 40

49

61

80

115

65

74

84

99

12 x 40

3.7 x 15.2

12 x 50

63

79

105

151

85

96

110

128

12 x 50

4.3 x 12.2

14 x 40

68

85

112

161

91

102

117

137

14 x 40

4.3 x 15.2

14 x 50

89

112

148

212

119

134

152

177

14 x 50

4.3 x 16.8

14 x 55

100

125

166

238

133

149

170

197

14 x 55

4.9 x 15.2

16 x 50

120

150

198

283

158

177

202

234

16 x 50

4.9 x 18.3

16 x 60

150

188

248

354

196

220

249

287

16 x 60

4.9 x 19.8

16 x 65

166

207

274

389

216

241

273

314

16 x 65

5.5 x 15.2

18 x 50

155

195

256

365

203

227

258

299

18 x 50

5.5 x 18.3

18 x 60

176

221

293

421

252

281

318

367

18 x 60

5.5 x 21.3

18 x 70

211

264

651

504

302

336

379

435

18 x 70

6.1 x 18.3

20 x 60

247

308

405

572

315

351

396

456

20 x 60

6.1 x 21.3

20 x 70

300

374

490

688

377

419

471

540

20 x 70

6.1 x 24.4

20 x 80

354

441

576

806

439

487

547

625

20 x 80

7.3 x 18.3

24 x 60

368

459

600

842

461

512

577

662

24 x 60

7.3 x 21.3

24 x 70

449

558

727

1013

551

611

686

784

24 x 70

7.3 x 24.4

24 x 80

432

660

857

1187

642

710

795

907

24 x 80

7.3 x 27.4

24 x 90

616

764

988

1361

734

809

905

1031

24 x 90

9.1 x 24.4

30 x 80

867

1070

1379

1892

1033

1269

1459

1606

30 x 80

9.1 x 27.4

30 x 90

1007

1240

1590

2169

1202

1472

1690

1860

30 x 90

9.1 x 30.5

30 x 100

1150

1411

1803

2447

1374

1678

1923

2116

30 x 100

9.1 x 33.5

30 x 110

1294

1584

2017

2726

1549

1886

2159

2374

30 x 110

(a) 1
tonne 1000kg: the capacity in tons (2000 lb) can be obtained by
multiplying the capacities in the table by 1.1 (b) moisture content in percent (wet basis)

No tests have been carried out at Guelph for grass. Based on work
done in the Netherlands grass consolidates somewhat more than alfalfa.
Capacities for grass silage may be estimated from Tables 1 and 2
by increasing the alfalfa silage capacities by 10, 15 and 20% for
moisture contents of 50, 60 and 70% respectively.

Table 3 presents silo capacities for high moisture corn. Capacities
for whole shelled and ground shelled corn, as well as ground ear
corn are shown. The capacity figures in Table 3 were calculated
on the basis of a friction coefficient of 0.6 an appropriate estimate
for concrete. High moisture corn is far less compressible than forage
and, therefore, friction has a much less effect on capacity. It
is recommended that for very smooth wall surfaces, such as glass-lined
steel or epoxy coated concrete, that the capacities in Table 3 be
increased by 3%.

(a) 1 tonne
1000kg: the capacity in tons (2000 lb) can be obtained by multiplying
the capacities in the table by 1.1 (b) moisture content in percent (wet basis)

The capacity tables are based on fully settled silage. The silo
height may be used if the silo is topped up one to two weeks after
initial filling. If this is not done the capacities in Tables 1,
2 and 3 should be determined on the actual settled depth of silage
after about two to three weeks rather than the silo height. Silage
may settle between 10 and 15% during the first two weeks after filling.
Another adjustment should be made if space in the top of silo allows
the piling up of material in a cone-shaped heap. To allow for this
pile, one-third of the height of the cone can be added to the settled
depth of the silage measured at the base of the cone.

There is no significant difference in capacity between topunloading
silos and those with sweep-arm bottom-unloading equipment. However,
the tables do not account for the large cavity formed with flail-type
bottom-unloading equipment and should not be used directly for silos
thus equipped.

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